1. Field of the Invention
The present invention generally relates to sound synthesis and more particularly to speech synthesis, synthesized by combining multiple sine wave harmonics.
2. Background Description
In many state of the art parametric voice coders (vocoders), e.g., sinusoidal vocoders and multi-band excitation vocoders, the output speech is synthesized as the sum of a number of sine waves. For voiced speech, the sine wave components correspond to different harmonics of the pitch frequency inside the speech bandwidth with actual or modeled phases. For unvoiced speech, the sine waves correspond to harmonics of a very low frequency (e.g., the lowest pitch frequency) with random phases. Mixed-voiced speech can be synthesized by combining pitch harmonics in the low-frequency band with random-phase harmonics in the high frequency band.
In a typical vocoder implementation (with 8 KHz sampling), the number of sine wave components needed to synthesize speech can range from 8 to 64. A straightforward synthesizer implementation involves generating each component with appropriate phase and amplitude and then, summing all the sine wave components. The computational complexity of this brute-force, straightforward approach is directly proportional to the number of sine wave components combined to make up the synthesized speech waveform. When the number of sine waves is high, the complexity is also high. Further, depending on the number of sine waves to be generated and combined, the computational load placed on the processor can vary significantly.
Thus there is a need for faster, simpler voice synthesis techniques and vocoders using such techniques especially to reduce the vocoder complexity and also to balance the processor load better while synthesizing complex speech.